Levin Lisa A, Neira Carlos, Grosholz Edwin D
Integrative Oceanography Division, Scripps Institution of Oceanography, La Jolla, California 92093-0218, USA.
Ecology. 2006 Feb;87(2):419-32. doi: 10.1890/04-1752.
Vascular plants strongly control belowground environments in most ecosystems. Invasion by vascular plants in coastal wetlands, and by cordgrasses (Spartina spp.) in particular, are increasing in incidence globally, with dramatic ecosystem-level consequences. We examined the trophic consequences of invasion by a Spartina hybrid (S. alterniflora x S. foliosa) in San Francisco Bay (USA) by documenting differences in biomass and trophic structure of benthic communities between sediments invaded by Spartina and uninvaded sediments. We found the invaded system shifted from an algae-based to a detritus-based food web. We then tested for a relationship between diet and tolerance to invasion, hypothesizing that species that consume Spartina detritus are more likely to inhabit invaded sediments than those that consume surface algae. Infaunal diets were initially examined with natural abundance stable isotope analyses and application of mixing models, but these yielded an ambiguous picture of food sources. Therefore, we conducted isotopic enrichment experiments by providing 15N-labeled Spartina detritus both on and below the sediment surface in areas that either contained Spartina or were unvegetated. Capitellid and nereid polychaetes, and oligochaetes, groups shown to persist following Spartina invasion of San Francisco Bay tidal flats, took up 15N from labeled native and invasive Spartina detritus. In contrast, we found that amphipods, bivalves, and other taxa less tolerant to invasion consumed primarily surficial algae, based on 13C enrichment experiments. Habitat (Spartina vs. unvegetated patches) and location of detritus (on or within sediments) did not affect 15N uptake from detritus. Our investigations support a "trophic shift" model for ecosystem response to wetland plant invasion and preview loss of key trophic support for fishes and migratory birds by shifting dominance to species not widely consumed by species at higher trophic levels.
维管植物在大多数生态系统中对地下环境具有很强的控制作用。维管植物入侵沿海湿地，尤其是米草属植物（互花米草属物种）的入侵，在全球范围内呈上升趋势，并产生了巨大的生态系统层面的影响。我们通过记录米草属杂交种（互花米草×多花米草）入侵美国旧金山湾后，入侵米草的沉积物和未入侵沉积物中底栖生物群落生物量和营养结构的差异，研究了其营养影响。我们发现入侵系统从以藻类为基础的食物网转变为以碎屑为基础的食物网。然后，我们测试了食物与入侵耐受性之间的关系，假设食用米草碎屑的物种比食用表层藻类的物种更有可能栖息在入侵沉积物中。最初，通过天然丰度稳定同位素分析和混合模型的应用来研究底栖动物的食物，但这些方法对食物来源的描述并不清晰。因此，我们通过在有米草或无植被的区域的沉积物表面和下方提供15N标记的米草碎屑进行同位素富集实验。小头虫科和沙蚕科多毛类动物以及寡毛类动物，在旧金山湾潮滩被米草入侵后仍能存活，它们从标记的本地和入侵米草碎屑中摄取了15N。相比之下，基于碳-13富集实验，我们发现对入侵耐受性较低的双壳类动物和其他分类群主要摄食表层藻类。栖息地（有米草与无植被斑块）和碎屑位置（沉积物表面或内部）并不影响从碎屑中摄取15N。我们的研究支持了生态系统对湿地植物入侵响应的“营养转移”模型，并预示着由于优势地位转向营养级较高的物种不广泛食用的物种，鱼类和候鸟将失去关键的营养支持。
